The invention described herein was made in the course of, or under a contract with the U.S. Atomic Energy Commission and/or its successor the Energy Research and Development Administration.
Labeled red blood cells (RBC's) have historically been used for imaging of the blood pool, including the placenta and for red cell mass determinations. Damaged labeled cells have been used for spleen imaging, and more recent applications have included blood pool dynamics and cardiac blood pool imaging, in which it is important to use imaging radiopharmaceuticals that are retained in the vascular system.
However, the application of .sup.99m Tc-labeled RBC's has been limited by the need to withdraw and label a sample of the patient's blood just prior to clinical study--a laborious task with existing labeling methods. Earlier preparation methods in which no reducing agents were used resulted in minimal success. Reductive methods using stannous ion produced the first dependable labeling method (see U.S. Pat. No. 3,725,295), but yields were limited to the 50-60% range which made it necessary to separate the unbound .sup.99m Tc before the labeled cells were injected. In later efforts, improved yields were achieved by decreasing the stannous ion content, but these systems required the preparation of fresh solutions just before use and considerable handling, sometimes including washing steps.